ITU-T G.709 defines one high-rate frame, i.e., an Optical channel Transport Unit-k (OTUk) (k=1, 2, 3, 4), so as to map a variety of client signals to one high-rate frame through a Time Division Multiplexing (TDM) scheme and transmit the mapped signals over an Optical Transport Network (OTN). One OTUk includes an Optical channel Data Unit (ODUk) and parity bytes for error correction of the ODUk. The ODUk includes a data overhead for information data containing a payload overhead and a payload, that is, an Optical channel Payload Unit (OPUk). k of OPUk/ODUk is defined as 0, 1, 2, 2e, 3, 4, . . . k=0 denotes a data rate of 1.25 Gbit/s, k=1 denotes a data rate of 2.5 Gbit/s, k=2/2e denotes a data rate of 10 Gbit/s, k=3 denotes a data rate of 40 Gbit/s, and k=4 denotes a data rate of 100 Gbit/s. OTU1 has a bit rate of approximately 2.666 Gbit/s, OTU2 has a bit rate of approximately 10.709 Gbits, OTU3 has a bit rate of approximately 43.018 Gbit/s, and OTU4 has a bit rate of approximately 111.8 Gbit/s. ITU-T defines only STM-16, STM-64 and STM-256 signals, which are SDH signals, as 2.5-Gbps, 10-Gbps and 40-Gbps client signals at a point of time when an OTU1, OTU2 or OTU3 signal is initially defined. In addition, ITU-T defines a mapping structure for mapping the SDH signals.
FIG. 1 illustrates an OTU3 frame structure and a frame structure for mapping an STM-256 signal to an OPU3 signal area.
An OTUk frame 100 includes a total of four rows each having 4,080 bytes. A front section of the OTUk frame 100 is an overhead area 110, and a rear section of the OTUk frame 100 is a forward error correction (FEC) parity byte area 130. Actual data is mapped to an OPUk payload area 120 and then transmitted. Due to a difference of a basic transmission rate, a fixed stuff byte area 121 having a total of 128 bytes exists in an OPU3 payload area on which the STM-256 signal is loaded, as illustrated in FIG. 1. No data is loaded on the fixed stuff byte area 121, and all fields of the fixed stuff byte area 121 are filled with 0. In FIG. 1, an OPUk OH area 111 and the OPUk payload area 120 correspond to OPUk. Although not illustrated in FIG. 1, when STM-16, which is a 10-Gbps SDH signal, is mapped to OTU2, the fixed stuff byte area having a total of 64 bytes is defined.
When STM64 and OTU3 are mapped in an asynchronous state, a Negative Justification (NJ) byte and a Positive Justification (PJ) byte are used. To be specific, if the incoming STM-64 signal speed is higher than the outgoing OPU-3 signal speed, that is, if signals to be transmitted are increased, actual data are additionally loaded on the NJ byte and then transmitted. On the contrary, if the incoming STM-64 signal speed is lower than the outgoing OPU3 signal speed, actual data are not loaded on the PJ byte. In this manner, if data are loaded and transmitted by appropriately using the NJ byte and the PJ byte, data may be transmitted by absorbing a transmission rate difference corresponding to several tens of ppm between the incoming STM-64 signal and the outgoing OPU3 signal. If a transmitter transmits the data using the NJ byte and the PJ byte, a receiver is required to know whether actual data is carried on the NJ byte and the PJ byte. Therefore, upon data transmission, the relevant information is loaded on a Justification Control (JC) byte and then transmitted. When STM-64 is mapped to OPU3, a lower 2-bit value of the JC byte is used. That is, if the lower 2-bit value of the JC byte is 00, NJ is a stuff byte and PJ is a data byte. If the lower 2-bit value of the JC byte is 01, NJ is a data byte and PJ is a data byte. If the lower 2-bit value of the JC byte is 11, NJ is a stuff byte and PJ is a stuff byte. A case of when the lower 2-bit value of the JC byte is 10 does not occur. At this time, the stuff byte is filled with 0.
However, as network client signals have been further diversified and OTNs have evolved to accommodate the network client signals, a typical Generic Mapping Procedure (GMP) has been required. In recent years, ITU-T G.709 defined as follows: client signals except for these SDH signals should be mapped through the GMP.
FIG. 2 illustrates a frame structure for mapping a 40-Gbps client signal, except for an STM-256 signal, to an OPU3 signal area.
An OTUk frame 200 is similar to the OTUk frame 100. However, the OTUk frame 200 has a frame structure designed such that an OPUk payload area 210 is divided on an M-byte basis and a client signal is mapped on an M-byte basis. The value of M is 1, 2, 8, 32 and 80 when k=0, 1, 2, 3 and 4, respectively. That is, when a 40-Gbps client signal is mapped to a 40-Gbps OPU3 payload area, the 40-Gbps client signal is divided and mapped on a 32-byte basis. One OPU3 frame has a total of 476 M-bytes.
The number of M-bytes in which the client signal is mapped to the OPU3 payload is referred to as Cm, and information is transmitted through a JC1 byte and a JC2 byte, as illustrated in FIG. 2. Due to the M-byte based mapping, there occurs a difference between Cm and Cn, which is the number of bits to be actually mapped in a client signal. Therefore, ΣCnD information is provided as an option that can further improve timing performance by correcting the difference between Cm and Cn.
As such, when the GMP mapping of the OPU3 signal is performed, the OPU3 signal is mapped on a 32-byte basis. Therefore, a stuff also occurs on a 32-byte basis. On the contrary, when the STM-256 signal is mapped to OPU3, a 16-byte fixed stuff is used, instead of a 32-byte basis. In some cases, the NJ byte should be used as data on a 1-byte basis, or the PJ byte should be used as a 1-byte stuff. That is, in order to accommodate all client signals, a data path for mapping only the STM-256 signal and data paths for mapping other 40-Gbps client signals should be separately provided.
Likewise, when the STM-64 signal, which is the 10-Gbps SDH signal, is mapped to the OPU2 signal, a 16-byte fixed stuff is used. The NJ byte should be used as data on a 1-byte unit, or the PJ byte should be used as a 1-byte stuff. On the contrary, other client signals except for the STM-64 signal are mapped on an M-byte basis (M=8). Therefore, a data path for an M-byte based mapping should be provided separately from an existing data path for mapping the STM-64 signal. Hence, the conventional frame structure may be unsuitable for implementing high-integration and high capacity because logic capacity, the use of which is unpredictable, should always be prepared, even unnecessarily.
Therefore, there is a need for an apparatus and a method for efficiently mapping a signal, without regard to a client signal.